1. Field of the Invention
The application relates to a method utilized in a wireless communication system and a communication device thereof, and more particularly, to a method of power reporting in a wireless communication system and a related communication device.
2. Description of the Prior Art
Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in Node B (NB) alone rather than in NB and RNC (Radio Network Controller) respectively, so that the system structure becomes simple.
The power headroom report is generated by a power headroom reporting (PHR) procedure, and is used to provide the serving eNB with information about the difference between the maximum UE transmission (TX) power and an estimated TX power for Uplink Share Channel (UL-SCH) and/or UL Control Channel. With power headroom (PH) information sent by the UE, the network can allocate radio resource to the UE and make schedule decision more efficiently. In the PHR procedure, the UE uses a MAC control element in a MAC protocol data unit (PDU) to carry PH information.
Toward advanced high-speed wireless communication system, such as transmitting data in a higher peak data rate, LTE-Advanced system is standardized by the 3rd Generation Partnership Project (3GPP) as an enhancement of LTE system. LTE-Advanced system targets faster switching between power states, improves performance at the cell edge, and includes subjects, such as bandwidth extension, coordinated multipoint transmission/reception (COMP), uplink multiple input multiple output (MIMO), etc.
For bandwidth extension, carrier aggregation (CA) is introduced to the LTE-Advanced system for extension to wider bandwidth, where two or more component carriers are aggregated, for supporting wider transmission bandwidths (for example up to 100 MHz) and for spectrum aggregation. According to carrier aggregation capability, multiple component carriers are aggregated into overall wider bandwidth, where the UE can establish multiple links corresponding to the multiple (downlink and uplink) component carriers for simultaneously receiving and transmitting.
In carrier aggregation, the UE only has one RRC connection with the network. At RRC connection establishment/re-establishment/handover, one serving cell provides the NAS mobility information, and at RRC connection re-establishment/handover, one serving cell provides the security input. This cell is referred to as a Primary serving cell (PCell). In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC) while in the uplink it is the Uplink Primary Component Carrier (UL PCC). In addition, cells other than the PCell are named secondary serving cell (SCell).
In LTE-A system (e.g. Rel-10), parallel physical uplink control channel (PUCCH) and physical uplink shared channel (PUSCH) transmission have been supported. Consequently, eNB should take into account PUCCH and PUSCH transmission power contributing to the UE current transmission power, so as to assist eNB to schedule PUSCH and PUCCH. Note that, for uplink resource, the PCell has PUSCH and PUCCH, but SCell only has PUSCH.
Note that, in LTE-A system, PH information shall be reported for all of the configured or activated uplink component carriers. This shall be well-known in the art, so it is not given herein. In addition, a maximum output power reporting for a configured/activated component carrier is agreed in LTE-A system. The maximum output power represents the allowed maximum output power for the UE on the configured/activated component carrier, and is used for calculation for the reported power headroom report for the configured/activated component carrier. However, the LTE-A system does not clearly specify how to report the maximum output power for the configured/activated component carrier. For example, what format shall be used for the maximum output power report and when the maximum output power report shall be reported is never concerned.